In production of semiconductor devices, micro-fabrication is generally carried out according to lithographic techniques by use of photoresist. The process of micro-fabrication comprises: forming a thin photoresist layer on a semiconductor substrate such as a silicon wafer; covering the layer with a mask pattern corresponding to the aimed device pattern; exposing the layer to active light such as ultraviolet (UV) light through the mask pattern; developing the exposed layer to obtain a photoresist pattern; and etching the substrate by use of the photoresist pattern as a protective film, to form a fine relief corresponding to the above pattern. Since the degree of integration in semiconductor devices has been increased recently, the exposure tends to be carried out by use of light of very short wavelength, such as KrF excimer laser light (wavelength: 248 nm), ArF excimer laser light (wavelength: 193 nm) or extreme UV light (wavelength: 13.5 nm). The above photolithographic process, however, often suffers from a problem of dimension precision degradation of the photoresist pattern. The dimension precision degradation is caused by a standing wave of light reflected from the substrate and/or by diffused reflection of the exposure light due to roughness of the substrate. Further, the resist layer may be adversely affected by gases given off from the substrate placed thereunder if the exposure is performed by use of light of very short wavelength, such as extreme UV light. To cope with those problems, many researchers are studying about a bottom anti-reflective coating provided between the photoresist layer and the substrate. The bottom anti-reflective coating is required to have various properties. For example, it is preferred for the bottom anti-reflective coating to largely absorb radiation used for exposure of the photoresist, to prevent diffuse reflection and the like so that the exposed and developed photoresist can have a cross section perpendicular to the substrate surface, and to be insoluble in solvents contained in the photoresist composition (namely, not to cause intermixing). The intermixing is particularly serious because it often gives adverse effects to the interface between the photoresist layer and the bottom anti-reflective coating. Accordingly, the intermixing is liable to make it difficult to control the pattern or shape of the photoresist.
The bottom anti-reflective coating is often formed from a thermo-crosslinkable composition, so as to prevent intermixing with the photoresist applied thereon. Consequently, the formed coating is generally insoluble in a developing solution used for development of the photoresist. Accordingly, in general, the anti-reflective coating must be removed by dry-etching before fabrication of the semiconductor substrate (see, for example, Patent document 1).
However, when the coating is removed by dry-etching, the photoresist tends to be partly removed together with the coating. This makes it difficult to keep enough thickness of the photoresist to fabricate the substrate.
In view of this, it is desired to provide a bottom anti-reflective coating which is sufficiently soluble in a developing solution used for development of the photoresist and hence which can be developed and removed together with the photoresist. In order to meet this desire, researchers have studied the bottom anti-reflective coating which is developable and removable together with the photoresist.
For example, it has been studied to make hydroxyl or carboxylic acid react with vinyl ether, so as to form a bottom anti-reflective coating developable and removable together with the photoresist (Patent document 2). However, this kind of method often has a problem of scum formed from a bottom anti-reflective coating in pattern formation.